* PM Abadi issued order to halt air strikes on civilians * Kerry in Cairo on regional tour to build a coalition * Islamic State controls a third of Iraq * Pope says global conflicts are "piecemeal" Third World War (Adds opposition statement) By Oliver Holmes and Jason Szep BAGHDAD/CAIRO, Sept 13 (Reuters) - Iraq's Shi'ite Prime Minister Haider al-Abadi said on Saturday that he had ordered his air force to halt strikes on civilian areas, following attacks by both Iraqi and U.S. jets in large areas of the country held by Islamic State fighters. ...